The invention relates to a method for, and apparatus used to weld thermoplastic materials in a continuous industrial process.
Looms used in fabric weaving processes are complex and have a number of creels, spools, spindles, reeds, drop wire slots, and tensioning festoons over which each individual filament or cord needs to be strung. This is a time consuming process for one cord, and since a typical bolt of fabric may have 600 to 2000 cords, more or less, stringing a loom for initial operation is a time consuming and difficult process.
Since filaments or cords are ordinarily supplied on a spool or a package which contains a limited supply of cord or filament, if some means were not provided to keep the loom strung, this process would have to be repeated each time a spool of filament or cord was depleted during weaving. Fortunately, in industrial looms, some efficiency is recaptured by tying a new spool of cord or filament to the end of a depleted spool of filament or cord before the depleted end of the cord or filament passes through the loom.
In recent years, monofilament materials, such as those described in U.S. Pat. No. 5,173,136 to Agarwal et al., and U.S. Pat. No. 5,743,975 to Sinopoli et al., have been gaining acceptance as a reinforcement material in composites. It has been found, however, that conventional cord tying or splicing does not work for monofilaments since monofilaments tend to be stiff and slippery. Knots are too bulky, snag on the equipment, and tend to slip. Also, monofilaments tend to slip out of conventional wrap splices.
In the weaving of monofilaments, especially heavy gauge nylon monofilaments, it is important to be able to attach one end of a filament to the end of another filament to 1) tie in successive creels or 2) repair a broken filament broken during weaving.
When it was found that conventional tying and splicing did not work for monofilaments, the inventors tested and collected data on a number of methods which might be used in place of tying or splicing and eventually decided to try to melt or fuse the individual monofilaments to each other at the loom. Once it was determined that specific monofilament materials can be fused by welding, the object of the invention was to develop a method and apparatus to provide an economical process for attaching the cords.
Although it is believed that other welding techniques will work, it was decided to use ultrasonic welding in the method.
Ultrasonic welding comprises the generation of high frequency (20 kHz or 40 kHz) mechanical vibrations which are transmitted to a welding horn. An ultrasonic welding horn applies a force at the surface of the materials to be bonded, and uses intermolecular friction at the interface to melt the material. A force is maintained against the material by the welding horn after the vibration is stopped, and upon cooling, a weld is produced.
Strother, in U.S. Pat. No. 3,184,363 describes an apparatus for splicing thermoplastic cords which comprise an apparatus having a die comprising a slot for holding thermoplastic material, wherein the bottom of the slot is concave and substantially semi-cylindrical. A tool in the apparatus is adapted to enter the slot and is concave and generally complimentary to the slot bottom. The apparatus has means for urging a tool into the die slot, and means for vibrating the tool at high frequency. The heat generated by the vibrations causes a thermoplastic material contained in the slot to melt.
Long et al. in GB 1,154,429 teach a process and apparatus for joining the ends of two textile threadlines. The apparatus comprises an ultrasonic apparatus is mounted on a casing 4 which surrounds a transducer stack. A straight groove 5 is cut across the face of a coupling stub 3 to locate and support threadlines being joined. A plunger 11 is mounted on a cam 7 for movement in and out of the stub groove 5. The cam 7 rotates on a pivot 17 at one end of an arm 9 which pivots on an axis on a support member 10. The plunger is slidably mounted in an arm 12 and bears against the surface of the cam through the action of a compression spring 13. The compression spring is opposed by a tensioning spring 14 attached to pivot 17. The pressure exerted by the plunger is determined by the tensioning of the springs.
Other objects of the invention will be apparent from the following description and claims.
A method for continuous operation of a fabric-weaving unit for weaving a fabric made from thermoplastic cords or monoflaments comprises the steps of (a) feeding a leading end of a first thermoplastic cord or monofilament (30a) into a weaving appartus through various reeds, drop wire slots, rolls and guides of the weaving apparatus and weaving the cord or monofilament (30a) into a fabric, (b) continuing processing of the cord or monofilament (30a) to a trailing end of the cord or monofilament (30a), (c) welding the trailing end of the cord or monofilament (30a) to a leading end of a second thermoplastic cord or monofilament (30), and (d) continuing the operation of the weaving unit by weaving the second thermoplastic cord or monofilament (30) into a fabric.
The method is illustrated using 2,000 to 20,000 dTex thermoplastic monofilaments as fabric material.
In a preferred embodiment, the method is used with cords or monofilaments comprising nylon.
The method is illustrated making a roll of fabric using 8 to 40 ends per inch (epi) cords or monofilaments in the warp direction and 1 to 8 epi pick cords in the weft direction, using an ultrasonic welder.
The method is carried out so that the monofilaments or cords (30,30a) are oriented such that at least one end thereof is fused in a weld (60), and preferably the weld (60) is oriented such that the lead end of the weld is fused so that a loose end (58) does not snag on any parts of the processing equipment.
Also provided is an apparatus for splicing thermoplastic cords or monofilaments comprising a welder (16) mounted on a fixture (14), said fixture (14) being rotatably mounted to a pole (12), said pole (12) being attached to a stand (15). The stand (15) is lightweight and can easily be moved, and may be otherwise adapted to be mobile, or in an alternative embodiment, may be fixed in position. In the illustrated embodiment, pole (12) is mounted vertically and the fixture (14) is adapted to rotate around the pole (12).
In the illustrated embodiment, the welder (16) is an ultrasonic welder. The welder (16) has a welding horn (18) which is used in conjunction with an anvil (20) for welding material. The anvil (20) may comprise a right feed cord alignment block (20a) or a left feed cord alignment block (20b).
Also provided is a mold for welding cord or filament ends comprising a top plate (32,48) and a lower plate (40,52), the top plate (32,48) being adapted to be pressed together the lower plate (40,52), wherein the top plate (32,48) has a groove (34,50) which transverses more than xc2xd the length of the top plate (32,48), and the lowerplate (40,52) has a groove (46,54) which traverses less than xc2xd the length of the lower plate (40,52) and an opening (44) at the termination of the groove (46,54). When the top plate (32,48) is aligned with and pressed together with the lower plate (40,52) to form a block (20) the groove (34,50) in the top plate (32,48) is in an opposite end of block (20) from the groove (46,54) in the lower plate (40,52), and the lower plate groove (34,50) overlaps with top plate groove (46,54) in the middle of block (20). An opening (44) in lower plate (40,52) is adapted to receive a welding horn (18).